The turnip is a root vegetable with a bitter taste, which was nonetheless widely cultivated in medieval times (since it will grow almost anywhere). It’s a period charge, found in the arms of Am Hard, c.1340 [Zurich 266].
A “turnip proper” in period would be mostly white (with some purple near the stem) with green leaves; the Society defines a “turnip proper” as (roughly) per fess wavy purpure and argent, slipped and/or leaved vert. Its leaves are to chief by default. See also fruit.
Jenifer of Squalid Manor bears: Or, a turnip purpure, leaved vert, distilling a goutte de sang.
Helena Caxton bears: Vert, a turnip argent.
Ysabelot Clarisse bears as a badge: A turnip bendwise proper.